1. Field of the Invention (Technical Field)
The invention relates to avionics navigation aids and more specifically to an onboard navigational system.
2. Background Art
The present state of the art includes navigation systems using Global Positioning System (GPS) sensors that are dependent upon receiving information from the GPS satellite constellation. GPS sensors may receive inaccurate or no data due to jamming, masking, spoofing, and other problems that communication systems are susceptible to. Other errors and/or dependencies are inherent to terrestrial-based and other navigation systems, and these errors can be reduced or eliminated using the present invention. Also, there is a need to reduce cost, reduce weight, and to have a system with a low probability of detection.
Some prior art systems include GPS-aided navigation systems, such as U.S. Pat. No. 6,167,347 entitled Vehicle Positioning Method And System Thereof, and U.S. Pat. No. 5,928,309 entitled Navigation/Guidance System For A Land-Based Vehicle.
A related invention is U.S. Pat. No. 6,218,980 entitled Terrain Correlation System. The present invention differs from U.S. Pat. No. 6,218,980 in that the present invention detects the highest elevation in given area sensed by the RADAR sensor, then compares the highest elevation sensed to those in a stored terrain data base; whereas U.S. Pat. No. 6,218,980 forms a terrain map of a given area illuminated and sensed by its RADAR, then compares the sensed terrain map to stored terrain maps. Other related patents are U.S. Pat. No. 6,014,103 entitled Passive Navigation System, and U.S. Pat. No. 5,574,649 entitled Position-Locating Method And Apparatus including corrections for elevational changes.
Also, cruise missiles have systems that updates the onboard navigation solution by correlating onboard, digitized terrain photos to photos taken in flight with an onboard camera, and by using GPS information. Present systems do not automatically and continuously compute a navigation solution using a RADAR sensor with terrain comparator. They integrate information from other sensors including cameras, RADAR, and GPS, and by using other methods like differential GPS.
Reliance on external communication systems and communication links including GPS and other space-based navigation systems, and terrestrial-based navigation systems, result in a higher probability of detection due to emissions from onboard sensors. Terrestrial-based systems are susceptible to data integrity issues and loss of communications. Systems using photographic sensors require adequate illumination of the terrain and are impaired by optical obstructions like dust, smoke, and clouds, and are easily detected and are very costly. Systems using terrain mapping sensors like terrain mapping RADAR are easily detected and very costly. These navigation solutions in state of the art systems are not autonomous and do not continuously compute improved solutions. These systems typically use strobe lights, satellites, space-based and ground-based transmitters, which are easily detected.
Although these prior art systems update the navigation solution, they are aperiodic and/or not continuous. For example, a GPS-aided navigation system typically updates its navigation solution once per second.
The novel feature of the present invention is the use of terrain features in all weather conditions for preparing a navigation solution. Terrain feature sensing and comparison with known terrain features has typically been applied for purposes of recognition, not for aiding a navigation solution. The present invention improves the precision and accuracy of other navigation solutions by automatically and continuously computing the solution for an airborne vehicle using only onboard sensors, information, and systems.
The effect of the invention can be realized today using the following process and systems. Under manual control, a terrain feature on a map is selected, then the operator determines the location of the terrain feature, then the actual terrain feature is detected using an onboard RADAR, then a processor computes the expected location of the terrain feature based on the current navigation solution, then processes the difference between the expected location and the relative location as determined by the RADAR in order to compute the navigation error in the current navigation solution. A processor then updates the onboard navigation system in order to minimize the computed navigation error.
In another example, the effect of the invention can be realized today using the following process and systems. Terrain photos are taken using an onboard camera, then a processor determines the expected position and orientation of digital terrain photos (stored onboard) based on the current navigation solution, then a processor computes the difference between the expected position and orientation of the stored terrain photo and the terrain photo acquired by the camera, then computes the navigation error in the current navigation solution, then a processor updates the onboard navigation system in order to minimize the computed navigation error.
A primary object of the present invention is to provide an accurate and precise navigation solution for airborne vehicles using only on board sensors.
Another object of the present invention is to provide an accurate and precise navigation solution for ground vehicles using only on board sensors.
Another object of the present invention is to provide an accurate and precise navigation solution for space vehicles using only on board sensors.
Another object of the present invention is to provide an accurate and precise navigation solution for surface vessels using only on board sensors.
Another object of the present invention is to provide an accurate and precise navigation solution for underwater vessels using only on board sensors.
Another object of the present invention is to provide an accurate and precise navigation solution for vehicles and vessels using multiple sensors and multiple navigation aids.
Yet another object of the present invention is to provide an all weather, low cost, autonomous and day/night navigation solution.
A primary advantage of the present invention is that it provides a higher accuracy and more precise measurements than those using a RADAR altimeter.
Another advantage of the present invention is that it provides a higher accuracy and more precise measurements than those using satellite-based navigation aids.
Another advantage of the present invention is that it provides a higher accuracy and more precise measurements than those using ground-based navigation aids.
Another advantage of the present invention is that it provides bearings to terrain features.
Another advantage of the present invention is that it is not subject to inertial drift problems due to availability of onboard mapped terrain databases.
Another advantage of the present invention is that it provides a higher accuracy and more precise measurements in all weather conditions and all lighting conditions.
Yet another advantage of the present invention is that it is light weight and inexpensive relative to present prior art systems.
Another advantage of the present invention is that it is jam resistant and virtually impossible to spoof.
Another advantage of the present invention is that it is more difficult to detect than present prior art systems.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.